High data rate communications from a ground-based antenna to a satellite in geosynchronous or geostationary earth orbit (GEO), medium earth orbit (MEO), or low earth orbit (LEO) may use a positioner on the antenna to allow movement that compensates for movements of the antenna and/or the satellite, so that the antenna remains pointed at the satellite. Antennas may include horns, reflectors, flat panel arrays, or various other radio frequency (RF) apertures to transmit and/or receive communications with the satellite. Such antenna positioners for an antenna may allow for movement, i.e. positioning of the antenna, about both an elevation axis and an azimuth axis. Where the antenna positioner is mounted to a mobile platform, such as an aircraft, vessel, or vehicle, the antenna positioner may need a range of 360° of rotation about the azimuth axis and a range of approximately 90° of rotation about the elevation axis to allow the antenna positioner to continue to point the antenna at the satellite during movement of the mobile platform. To allow unrestricted movement of the mobile platform, the antenna positioner may need to allow for continuous (free) rotation of the antenna about the azimuth axis.
The described antenna positioners need a way to drive the rotation about the azimuth axis and a way to drive the rotation about the elevation axis. Several mechanisms have been proposed for elevation over azimuth (EL/AZ) type designs, where an antenna element may rotate about the elevation axis of a mount of the antenna positioner, and the mount and antenna element together may rotate about the azimuth axis.
One system to drive an antenna positioner is to connect a first drive motor to an azimuth drive shaft to drive rotation of the antenna positioner about the azimuth axis. Then, to drive the antenna positioner about the elevation axis, a second drive motor is connected to the elevation axis to drive rotation of the antenna positioner about the elevation axis. Such drive motors typically require several different electrical connections for power, control, etc. For the azimuth motor, which may be fixedly mounted to the mobile platform along with the stationary portions of the antenna positioner, such electrical connections may simply be metal wires. However, the drive motor for the elevation axis rotates about the azimuth axis along with the rotatable portions of the antenna positioner. If metal wires are used for this drive motor, as the drive motor rotates about the azimuth axis, the wires may bind, restricting azimuth rotation of the antenna positioner and preventing free rotation of the antenna positioner about the azimuth axis during movement of the mobile platform.
One mechanism to provide an electrical connection to an elevation motor is to use a rotary mechanism, such as a rotary joint employing a slip ring, e.g. a brush block slip ring, to pass RF, power, and control signals across the azimuth rotating interface for the elevation motor. However, such rotary mechanisms have several disadvantages, including relatively large size and cost, as well as somewhat poor reliability, e.g. one or both of the brushes of the slip ring and the rotary joint may wear out. In addition, rotary joints may have large insertion losses.